The present invention relates to an air bag made up of resin sheets which are bonded each other. The purpose of an air bag device is to protect an occupant by deploying an air bag when a vehicle comes into collision. Conventionally, an air bag is typically made of woven textile of fiber, such as polyamide fiber, surfaced with a silicone rubber coating. In recent years, however, an air bag made of resin films (Japanese Unexamined Patent Publication No. H2-31965/1990) and an air bag made of elastomer (Japanese Unexamined Patent Publication No. H4-266544/1992) have been proposed as alternatives to the conventional air bag.